Small electronics such as the popular fitness trackers and smartwatches are not easy to take apart and recycle. When disposed of, the devices are sent into toxic waste streams. According to ACS Applied Materials & Interfaces, researchers have developed a two-metal nanocomposite for circuits that breaks down when submerged in water.
The constant tech innovation and invitation to replace devices for a newer version leads to millions of tonnes of electronic waste every year. Recycling can reduce the volume of electronic waste and is mandatory in many places. But, it often isn’t considered worth the effort to recycle small consumer electronics because their parts must be recovered by hand, and some processing steps, such as open burning and acid leaching, can cause health issues and environmental pollution.
Researcher Xian Huang and colleagues previously developed a zinc-based nanocomposite that dissolved in water for use in temporary circuits, but it wasn’t conductive enough for consumer electronics. The researchers modified the zinc-based nanocomposite to make it robust enough to endure everyday use, by adding silver nanowires, making it highly conductive. Then, they screen-printed the metallic solution onto pieces of poly(vinyl alcohol), a polymer that degrades in water, and solidified the circuits by applying small droplets of water that facilitate chemical reactions and then evaporate.
This way, the team built a smartwatch with multiple nanocomposite-printed circuit boards inside a 3D printed poly(vinyl alcohol) case. The smartwatch had sensors that correctly measured a person’s heart rate, blood oxygen levels and step count, and sent the information to a cellphone app via a Bluetooth connection. The outer casing was able to resist sweat, but once the whole device was fully immersed in water, both the polymer case and circuits dissolved completely within 40 hours. Only the watch’s components remained, such as an organic light-emitting diode (OLED) screen and microcontroller, as well as resistors and capacitors that had been integrated into the circuits. The researchers say the two-metal nanocomposite can be used to produce short-lived devices with performance matching that of commercial models, which could go a long way toward solving the challenges of small electronics waste.